Electron Spin Resonance Super-Hyperfine Splitting Study of Polycrystalline Niobocene and Vanadocene Dichlorides

1996 ◽  
Vol 61 (12) ◽  
pp. 1767-1772 ◽  
Author(s):  
Jana Holubová ◽  
Zdeněk Černošek ◽  
Ivan Pavlík
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Unpaired Electron ◽  
Hyperfine Splitting ◽  
Hyperfine Coupling Constant ◽  
Esr Spectra ◽  
Coupling Constant ◽  
Average Value ◽  
Spin Resonance ◽  
Vanadocene Dichloride

The electron spin resonance (ESR) spectra of niobocene and vanadocene dichlorides were studied on the title compounds prepared as magnetically diluted species in polycrystalline form. The resolved super-hyperfine splitting of anisotropic ESR spectra of both studied compounds was firstly observed. Computer simulation confirmed that this super-hyperfine splitting is due to interaction of unpaired electron with nuclear spin of two chlorine ligands. Average value of super-hyperfine coupling constant is 13.3 MHz for niobocene dichloride. For vanadocene dichloride, it is estimated to be in the range of 6-10 MHz. It corresponds approximately to 10% delocalization of metal unpaired electron spin density onto chlorine ligands in case of niobocene dichloride and to 4-7% delocalization in case of vanadocene dichloride.

Electron Spin Resonance Linewidth Studies of Vanadyl Tetraphenylporphyrin

1993 ◽  
Vol 58 (6) ◽  
pp. 1294-1298
Author(s):  
Ali H. Al-Mowali ◽  
Alhan D. Girgees
Keyword(s):  
Electron Spin Resonance ◽  
Unpaired Electron ◽  
Hyperfine Coupling ◽  
Hyperfine Coupling Constant ◽  
Esr Spectra ◽  
Coupling Constant ◽  
Electron Spin Resonance Linewidth ◽  
Isotropic Hyperfine Coupling ◽  
Spin Resonance ◽  
Line Widths

The linewidths of the hyperfine components of the ESR spectra of vanadyl tetraphenylporphyrin in liquid toluene have been measured as a function of temperature and analyzed in detail. This has allowed the separate contributions to the observed ESR line widths from spin rotational, g tensor anisotropy, hyperfine anisotropy and unresolved nitrogen hyperfine coupling to be evaluated. These results have been used to estimate the size of the nitrogen isotropic hyperfine coupling constant and thus the extent of delocalization of the unpaired electron onto the nitrogen atoms.

An ESR and calorimetric study of iron oolitic samples from the Northampton ironstone

Clay Minerals ◽  
1990 ◽  
Vol 25 (3) ◽  
pp. 303-311 ◽  
Author(s):  
A. U. Gehring ◽  
R. Karthein
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Hyperfine Splitting ◽  
Esr Spectroscopy ◽  
Thermal Conversion ◽  
Esr Spectra ◽  
Calorimetric Study ◽  
Calorimetric Methods ◽  
Mineral Phases ◽  
Spin Resonance

AbstractElectron spin resonance (ESR) spectroscopy and calorimetric methods were used to characterize conversion processes in multimineral samples from the Northampton ironstone (NIS) at temperatures between 25°C and 800°C. The beginning of the thermal conversion processes can be determined by the formation of asymmetric ESR spectra with g ≈ 2 at 250°C. The breakdown of the berthierine structure between 250°C and 520°C is indicated by the disappearance of the hyperfine splitting in the Mn2+ spectrum and the formation of magnetite. The decomposition of siderite and calcite was found by calorimetric methods at 580°C and 700°C, respectively. The hematite formation between 550°C and 800°C is explained by the decomposition of siderite but also by the oxidation of previously formed magnetite. The occurrence of hematite as the dominant ferric oxide at 800°C signifies the end of the conversion process of the major mineral phases in the NIS samples.

Non-Equivalence and Inverse Allosteric Response of the α and β Chains in Haemoglobins. An Electron Spin Resonance Study of NO-Ligated Hb Kansas

1976 ◽  
Vol 31 (11-12) ◽  
pp. 664-674 ◽  
Author(s):  
Hans Twilfer ◽  
Klaus Gersonde
Keyword(s):  
Electron Spin Resonance ◽  
Spin Density ◽  
Electron Spin ◽  
Hyperfine Splitting ◽  
Esr Spectra ◽  
Type I ◽  
Type Ii ◽  
High Ph ◽  
Spin Resonance ◽  
Spectral Components

Abstract The electron spin resonance (ESR) spectra of 15NO- and 14NO-ligated Hb Kansas have been measured at 77 K in the range of pH 5 to 10. At low pH the ESR spectrum is the composite of a type I and a type II spectrum which changes to another composite of a type I and type II spectrum at high pH. For the definition of type I and type II spectra and the correlation of these types with two tertiary conformation states see Overkamp et al., Z. Naturforsch. 31 c , 524 [1976]. Both, the type I and the type II spectra observed at low and high pH respectively are different with regard to g-tensors and hyperfine-splitting constants. Therefore at intermediate pH values the ESR spectra of NO-Hb Kansas are the composites of four spectral components. The assignments of the four spectral components to the a and the β chains are arrived at from the comparison of the ESR spectra of the α2Mmet β2NO and of the α2MNO β2NO species of Hb M Iwate. α and β chains are both characterized by a pH-dependent spectral transition from a type I to a type II spectrum. The chains are non-equivalent with regard to both the type I and the type II spectra. The type I spectra assigned to the a and the β chains are characterized by g*zz = 2.0095 with a hyperfine splitting of a*zz (15NO) = 2.36 mT and gzz = 2.0085 with a hyperfine splitting of a*zz(15NO) = 2.41 mT respectively. The type II spectra assigned to the α and the β chains are characterized by g*′zz = 2.005 and a hyperfine splitting of a*′zz (15NO) = 3.07 mT and g′zz=2.005 and a hyperfine splitting of a′zz (15NO) = 3.31 mT. The change of the hyperfine splitting at gzz during the transition from type I to type II corresponds to an increase of the spin density at the NO by about 25% in both types of chains. Comparison of type I spectra of the NO-ligated α and β chains respectively demonstrates that the spin density at the NO is larger in the β chains than in the oc chains. The spectral types are correlated with functional states defined by the kinetics of NO-binding. Binding of inositol hexaphosphate has no influence on the ESR spectra in the whole range of pH as it is expected if NO-Hb Kansas is in the quaternary T structure.

Electron Spin Resonance Spectrum of the tert-Butylperoxy Radical, B16O17O•

1972 ◽  
Vol 50 (12) ◽  
pp. 1981-1983 ◽  
Author(s):  
J. A. Howard
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin Resonance Spectrum ◽  
Electron Spin ◽  
Hyperfine Coupling ◽  
Resonance Spectrum ◽  
Hyperfine Coupling Constant ◽  
Coupling Constant ◽  
Tert Butyl ◽  
Spin Resonance ◽  
Butyl Peroxide

A tert-butylperoxy radical specifically labelled with 17O on the terminal oxygen has been prepared by photolysis of di-tert-butyl peroxide in perdeuterocyclopentane containing 17O enriched oxygen. The value of the 17O hyperfine coupling constant is 23.45 G.

FREE RADICALS OF BIOLOGICAL INTEREST: PART II. ELECTRON SPIN RESONANCE (ESR) SPECTRA OF 2537 A IRRADIATED AMINO ACIDS

1967 ◽  
Vol 45 (12) ◽  
pp. 1831-1839 ◽  
Author(s):  
W. F. Forbes ◽  
P. D. Sullivan
Keyword(s):  
Amino Acids ◽  
Electron Spin Resonance ◽  
Electron Spin ◽  
Hydrogen Abstraction ◽  
Esr Spectra ◽  
Side Chain ◽  
Biological Interest ◽  
Spin Resonance ◽  
Cyclohexadienyl Radical ◽  
Secondary Radical

Polycrystalline amino acids, when irradiated with 2537 Å light, afford a variety of electron spin resonance signals. These signals are generally stable at room temperature for relatively long periods of time. For a number of the spectra obtained, there is evidence that more than one radical species contributes to the observed spectra. The signals obtained frequently differ from those obtained on exposure to ionizing radiation. The postulated species formed can often be visualized as being formed by effective hydrogen abstraction from the alkyl-substituted tertiary carbon atom or from the —OH, —SH or —NH group contained in the side chain. For L-phenylalanine a secondary radical is obtained, which is ascribed to a cyclohexadienyl radical.

Electron spin resonance observations of photochemically generated contact ammonium ion-pairs of fluoro-substituted ketones

1979 ◽  
Vol 57 (5) ◽  
pp. 600-602 ◽  
Author(s):  
K. S. Chen ◽  
T. Foster ◽  
J. K. S. Wan
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Ion Pairs ◽  
Esr Spectra ◽  
Ammonium Ion ◽  
Spin Resonance ◽  
Photochemical Systems

Contact radical ion-pairs of ammonium and fluoro-substituted ketones were generated in photochemical systems and their here-to-fore elusive esr spectra were characterized.

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